Recently, it was determined that the use of dichlorodifluoromethane (CFC12) for refrigerators and automotive air conditioners would be legally banned in order to protect the ozone layer, and also that the use of chlorodifluoromethane (HCFC22) is about to be legally regulated. Thus, hydrofluorocarbons which do not destroy the ozone layer, such as difluoromethane (HFC32), have been developed as substitutes for HCFC22.
As refrigeration oils which can be used in combination with the hydrofluorocarbons, there have been so far reported esters, carbonates, polyalkylene glycols, etc. Among them, the esters are most preferable for the following reasons: (1) They have a high electric insulating property; (2) they have a low hygroscopicity; and (3) they do not generate non-condensed gases, such as carbon dioxide, etc. Therefore, the esters have started to be used in a compression refrigerating machine for electric refrigerators, etc., in which 1,1,1,2-tetrafluoroethane (HFC134a) is used as a refrigerant.
Examples of such esters are numerously disclosed, for instance in British Patent No. 2,216,541, U.S. Pat. No. 5,021,179. European Patent Publication Nos. 445,610, 445,611, 458,584 and 468,729, International Publication No. WO 90/12849 (corresponding to Japanese Patent Unexamined Publication No. 505602/1991), Japanese Patent Laid-Open Nos. 88892/1991, 128991/1991, 128992/1991, 179091/1991, 200895/1991, 200896/1991, 217494/1991, 227397/1991, 252497/1991, 4294/1992, 20597/1992, 25595/1992, 72390/1992, 85396/1992, 88096/1992, 91194/1992, etc. However, all of these patent publications teach only the esters used in combination with 1,1,1,2-tetrafluoroethane and they are completely silent with regard to the use of difluoromethane (HFC32). Specifically, the esters which can be used in combination with difluoromethane are not taught therein. Also, in all of the Examples of these publications, only the use of 1,1,1,2-tetrafluoroethane is disclosed.
Difluoromethane (HFC32) is a preferred refrigerant, from the viewpoint of refrigerating capacity, as a refrigerant for room air conditioners and package air conditioners. However, since difluoromethane (HFC32) has a higher polarity than 1,1,1,2-tetrafluoroethane (HFC134a), it poses a compatibility problem at a low temperature with the esters presently used in a compression refrigerating machines for electric refrigerators, etc. in which 1,1,1,2-tetrafluoroethane (HFC134a) is used as a refrigerant.
Therefore, a development of an ester having an excellent compatibility with difluoromethane (HFC32) is in demand in the field of art.